This invention relates to toolholders. It is especially concerned with a body having at least one cutting insert seat on one end and a shank receivable in the bore of a tool support member on the other end. Such tools are used in the cutting and shaping of workpieces where it is important that the toolholder be held in a rigid manner so that both movement and vibration are minimized during the metalcutting operation.
Many devices in the prior art have proven to be successful in this regard and are exemplified by McCreery U.S. Pat. Nos. 3,498,653; McCray et al 4,135,418; Heaton et al 4,197,771; and Friedline 4,350,463. The foregoing devices are concerned with the use of ball-like locking elements to hold the shank of a toolholder in the bore of the tool support member.
One drawback common to the foregoing designs is the feature that the locking elements in each must abut against at least one surface during locking that is not similar in size and shape to the locking element abutment surface. This produces small contact areas with high contact stresses leading to plastic deformation of the locking elements and the surfaces they abut against each time the toolholder is locked onto a support member. After many repeated uses, the deformation in the locking elements and the surfaces they abut against can lead to a reduction in the rigidity of the toolholder, thus shortening its useful lifetime.
There is, therefore, clearly a need for a toolholder and a toolholder assembly design which has a longer lifetime. This design must, however, be capable of being easily and accurately manufactured. It should also be capable of being compactly sized so that it can be used in a wide range of applications, including small diameter boring bars.